Titan IV Inertial Upper Stage (IUS)
- Length: 17ft
- Diameter: 9.5ft
- Propellant: HTPB (hydroxyl terminated poly-butadine) solid propellant
- Propulsion: 2 Chemical Systems Division Solid Rocket Motors
- 1st Stage Thrust: 45,600 lbs.
- 2nd Stage Thrust: 18,500 lbs.
- 1st Stage ISP: 295.5 sec.
- 2nd Stage ISP: 303.5 sec.
The Inertial Upper Stage (IUS), with Boeing as the prime contractor, is a key element of the National Space Transportation System developed by the Air Force and NASA. The IUS offers spacecraft users an upper stage with built-in flexibility and adaptability for integration with the Space Shuttle and the Titan IV launch vehicles. The IUS can accurately deliver spacecraft into a wide range of earth orbits beyond the launch vehicle's capability.
The IUS Program began development in 1976; and its first flight was on a Titan launch vehicle in 1982. As of that time, XX payloads have been successfully delivered beyond low earth orbit with unprecedented accuracy and reliability.
The IUS is the only upper stage in the Nation's inventory featuring fully redundant avionics. All spacecraft launched by the IUS have reached their operational orbits. This success record underscores the prudence of the government's decision to develop and continue to use the highly reliable, solid propulsion IUS. Spacecraft managers who have used the IUS for their high value missions have done so in recognition of the superior reliability of the IUS. It has, and will continue to deliver Department of Defense payloads into a variety of earth orbits. NASA's Tracking and Data Relay Satellites (TDRS), which are also part of the National Space Transportation Svstem. have been placed in geosynchronous orbit by the IUS. In addition, thc spacecraft for NASA's Magellan, Galileo, and Ulysses planetary missions were delivered to their interplanetary trajectories by the IUS with unparalleled accuracy.
The program has received numerous citations and awards, including the prestigious Federation Aeronautic International (FAI) Diploma D'Honneur for Astronautics in 1991. The award was presented "For the design, development, manufacturing and successful operations achievements of the IUS..." The fundamental elements of the IUS are: two high-performance, solid-fuel rocket motors; an interstage; an equipment support section that includes the redundant avionics for guidance, navigation, and communications; a reaction control system; and an electrical power system.
The two-stage IUS vehicle can deliver 5,100 pounds into geosynchronous orbit. Performance improvement options have been identified which will accommodate heavier payloads. Current activities to upgrade the IUS guidance and navigation system with state-of-the-art technology will provide a system which will serve our Nation well into the next century.
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